We have a hybrid WCF and ASMX web service currently being used on a decent sized project. Now, most of time everything works perfectly fine, however on rare occasions and seemingly randomly, the web service begins to block calls which returns a 401 Unauthorized error back to the page in question. It seems to be the ASMX service calls that are causing this, but given that's it doesn't occur often and isn't reproducible I can't say this for certain.
The error goes away after an IIS reset, and at least on one occasion it eventually just went away on it's own. We use Windows Authentication as the credential type with anonymous access disabled.
Anyone have any ideas about why this might be occuring?